Kernel [[Wikipedia:Mode-setting|Mode Setting]] (KMS) is a method for setting display resolution and depth in the kernel space rather than user space.

Kernel [[Wikipedia:Mode-setting|Mode Setting]] (KMS) is a method for setting display resolution and depth in the kernel space rather than user space.

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== Background ==

== Background ==

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Previously, setting up the video card was the job of the X server. Because of this, it was not easily possible to have fancy graphics in virtual consoles. Also, each time a switch from X to a virtual console was made ({{Keypress|Ctrl+Alt+F1}}), the server had to give control over the video card to the kernel, which was slow and caused flickering. The same "painful" process happened when the control was given back to the X server ({{Keypress|Ctrl+Alt+F7}}).

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Previously, setting up the video card was the job of the X server. Because of this, it was not easily possible to have fancy graphics in virtual consoles. Also, each time a switch from X to a virtual console was made ({{ic|Ctrl+Alt+F1}}), the server had to give control over the video card to the kernel, which was slow and caused flickering. The same "painful" process happened when the control was given back to the X server ({{ic|Ctrl+Alt+F7}}).

With Kernel Mode Setting (KMS), the kernel is now able to set the mode of the video card. This makes fancy graphics during bootup, virtual console and X fast switching possible, among other things.

With Kernel Mode Setting (KMS), the kernel is now able to set the mode of the video card. This makes fancy graphics during bootup, virtual console and X fast switching possible, among other things.

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=== Late KMS start===

=== Late KMS start===

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[[Intel]], [[Nouveau]] and [[ATI]] drivers already enable KMS automatically for all chipsets. So you need not install it manually.

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[[Intel]], [[Nouveau]] and [[ATI]] drivers already enable KMS automatically for all chipsets, so you need not install it manually.

The proprietary [[NVIDIA]] and [[AMD Catalyst]] drivers do not use the open driver stack. In order to use KMS you should replace them with open source drivers.

The proprietary [[NVIDIA]] and [[AMD Catalyst]] drivers do not use the open driver stack. In order to use KMS you should replace them with open source drivers.

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See [[Fonts#Changing_the_default_font | changing the default font]] for how to change your console font to a large font. Terminus font in [community] is available in many sizes, including larger sizes.

See [[Fonts#Changing_the_default_font | changing the default font]] for how to change your console font to a large font. Terminus font in [community] is available in many sizes, including larger sizes.

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===Issue upon bootloading and dmesg===

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===Problem upon bootloading and dmesg===

Polling for connected display devices on older systems can be quite expensive. Poll will happen periodically and can in worst cases take several hundred milliseconds, depending on the hardware. This will cause visible stalls, for example in video playback. These stalls might happen even when your video is on HDP output but you have other non HDP outputs in your hw configuration. If you experience stalls in display output occurring every 10 seconds, disabling polling might help.

Polling for connected display devices on older systems can be quite expensive. Poll will happen periodically and can in worst cases take several hundred milliseconds, depending on the hardware. This will cause visible stalls, for example in video playback. These stalls might happen even when your video is on HDP output but you have other non HDP outputs in your hw configuration. If you experience stalls in display output occurring every 10 seconds, disabling polling might help.

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In case that your monitor/TV is not sending the appropriate [[Wikipedia:EDID|EDID]] data or similar problems, you will notice that the native resolution is not automatically configured or no display at all. The kernel has a provision to load the binary EDID data, and provides as well data to set four of the most typical resolutions.

In case that your monitor/TV is not sending the appropriate [[Wikipedia:EDID|EDID]] data or similar problems, you will notice that the native resolution is not automatically configured or no display at all. The kernel has a provision to load the binary EDID data, and provides as well data to set four of the most typical resolutions.

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If you have the EDID file for your monitor the process is easy. If you don't have, you can either use one of the built-in resolution-EDID binaries (or generate one during kernel compilation, [http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/EDID/HOWTO.txt more info here]) or build your own EDID.

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If you have the EDID file for your monitor the process is easy. If you do not have, you can either use one of the built-in resolution-EDID binaries (or generate one during kernel compilation, [http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/EDID/HOWTO.txt more info here]) or build your own EDID.

In case you have an EDID file (e.g. extracted from Windows drivers for your monitor), create a dir {{ic|edid}} under {{ic|/lib/firmware}}:

In case you have an EDID file (e.g. extracted from Windows drivers for your monitor), create a dir {{ic|edid}} under {{ic|/lib/firmware}}:

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video=<conn>:<xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m][eDd]

video=<conn>:<xres>x<yres>[M][R][-<bpp>][@<refresh>][i][m][eDd]

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*<conn>: Connector, e.g. DVI-I-1, see your kernel log.

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*<conn>: Connector, e.g. DVI-I-1, see {{ic|/sys/class/drm/}} for available connectors

*<xres> x <yres>: resolution

*<xres> x <yres>: resolution

*M: compute a CVT mode?

*M: compute a CVT mode?

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You can override the modes of several outputs using "video" several times, for instance, to force DVI to 1024x768 at 85 Hz and TV-out off:

You can override the modes of several outputs using "video" several times, for instance, to force DVI to 1024x768 at 85 Hz and TV-out off:

video=DVI-I-1:1024x768@85 video=TV-1:d

video=DVI-I-1:1024x768@85 video=TV-1:d

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To get the name and current status of connectors, you can use the following shell oneliner:

You may want to disable KMS for various reasons, such as getting a blank screen or a "no signal" error from the display, when using the Catalyst driver, etc. To disable KMS, add {{ic|nomodeset}} as a kernel parameter. See [[Kernel parameters]] for more info.

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You may want to disable KMS for various reasons, such as getting a blank screen or a "no signal" error from the display, when using the Catalyst driver, etc. To disable KMS add {{ic|nomodeset}} as a kernel parameter. See [[Kernel parameters]] for more info.

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Along with {{ic|nomodeset}} kernel parameter, for Intel graphics card you need to add {{ic|1=i915.modeset=0}} and for Nvidia graphics card you need to add {{ic|1=nouveau.modeset=0}}. For Nvidia Optimus dual-graphics system, you need to add all the three kernel parameters (i.e. {{ic|1="nomodeset i915.modeset=0 nouveau.modeset=0"}}).

{{Note|Some [[Xorg]] drivers will not work with KMS disabled. See the wiki page on your specific driver for details.}}

{{Note|Some [[Xorg]] drivers will not work with KMS disabled. See the wiki page on your specific driver for details.}}

Revision as of 21:23, 12 February 2014

Kernel Mode Setting (KMS) is a method for setting display resolution and depth in the kernel space rather than user space.

The Linux kernel's implementation of KMS enables native resolution in the framebuffer and allows for instant console (tty) switching. KMS also enables newer technologies (such as DRI2) which will help reduce artifacts and increase 3D performance, even kernel space power-saving.

Note: The proprietary nvidia and catalyst drivers also implement kernel mode-setting, but as they do not use the built-in kernel implementation, they lack an fbdev driver for the high-resolution console.

Contents

Background

Previously, setting up the video card was the job of the X server. Because of this, it was not easily possible to have fancy graphics in virtual consoles. Also, each time a switch from X to a virtual console was made (Ctrl+Alt+F1), the server had to give control over the video card to the kernel, which was slow and caused flickering. The same "painful" process happened when the control was given back to the X server (Ctrl+Alt+F7).

With Kernel Mode Setting (KMS), the kernel is now able to set the mode of the video card. This makes fancy graphics during bootup, virtual console and X fast switching possible, among other things.

Installation

At first, note that for any method you use, you should always disable:

Any "vga=" options in your bootloader as these will conflict with the native resolution enabled by KMS.

Any "video=" lines that enable a framebuffer that conflicts with the driver.

Late KMS start

Intel, Nouveau and ATI drivers already enable KMS automatically for all chipsets, so you need not install it manually.

The proprietary NVIDIA and AMD Catalyst drivers do not use the open driver stack. In order to use KMS you should replace them with open source drivers.

Early KMS start

To load KMS as early as possible in boot process, add the module radeon (for ATI/AMD cards), i915 (for Intel integrated graphics) or nouveau (for Nvidia cards) to the MODULES line in /etc/mkinitcpio.conf. For example:

/etc/mkinitcpio.conf

MODULES="... i915 ..."

If you are using a custom EDID file (not applicable for the built-in resolutions), you should embed it into initramfs as well:

/etc/mkinitcpio.conf

FILES="/lib/firmware/edid/your_edid.bin"

Rebuild your kernel image (refer to the mkinitcpio article for more info):

# mkinitcpio -p <name of your kernel preset; e.g. linux>

Troubleshooting

My fonts are too tiny

See changing the default font for how to change your console font to a large font. Terminus font in [community] is available in many sizes, including larger sizes.

Problem upon bootloading and dmesg

Polling for connected display devices on older systems can be quite expensive. Poll will happen periodically and can in worst cases take several hundred milliseconds, depending on the hardware. This will cause visible stalls, for example in video playback. These stalls might happen even when your video is on HDP output but you have other non HDP outputs in your hw configuration. If you experience stalls in display output occurring every 10 seconds, disabling polling might help.

If you see an error code of 0x00000010 (2) while booting up, (You will get about 10 lines of text, the last part denoting that error code), then add the following line into /etc/modprobe.d/modprobe.conf:

options drm_kms_helper poll=0

Forcing modes and EDID

Note: This section is a WIP. Improvements and corrections are more than welcome

In case that your monitor/TV is not sending the appropriate EDID data or similar problems, you will notice that the native resolution is not automatically configured or no display at all. The kernel has a provision to load the binary EDID data, and provides as well data to set four of the most typical resolutions.

If you have the EDID file for your monitor the process is easy. If you do not have, you can either use one of the built-in resolution-EDID binaries (or generate one during kernel compilation, more info here) or build your own EDID.

In case you have an EDID file (e.g. extracted from Windows drivers for your monitor), create a dir edid under /lib/firmware:

# mkdir /lib/firmware/edid

and then copy your binary into the /lib/firmware/edid directory.

To load it at boot, specify the following in the kernel command line:

drm_kms_helper.edid_firmware=edid/your_edid.bin

You can also specify it only for a specified connection:

drm_kms_helper.edid_firmware=VGA-1:edid/your_edid.bin

For the four built-in resolutions, see table below for the name to specify:

Resolution

Name to specify

1024x768

edid/1024x768.bin

1280x1024

edid/1280x1024.bin

1600x1200 (kernel 3.10 or higher)

edid/1600x1200.bin

1680x1050

edid/1680x1050.bin

1920x1080

edid/1920x1080.bin

If you are doing early KMS, you must include the custom EDID file in the initramfs or you will run into problems.

You can also construct your own EDID with the makefile included in the Documentation/EDID sources of the kernel. The full information can be read here and there.

Warning: The method described below is somehow incomplete because e.g. Xorg does not take into account the resolution specified, so users are encouraged to use the method described above; however, specifying resolution with video= command line may be useful in some scenarios

Disabling modesetting

You may want to disable KMS for various reasons, such as getting a blank screen or a "no signal" error from the display, when using the Catalyst driver, etc. To disable KMS add nomodeset as a kernel parameter. See Kernel parameters for more info.

Along with nomodeset kernel parameter, for Intel graphics card you need to add i915.modeset=0 and for Nvidia graphics card you need to add nouveau.modeset=0. For Nvidia Optimus dual-graphics system, you need to add all the three kernel parameters (i.e. "nomodeset i915.modeset=0 nouveau.modeset=0").

Note: Some Xorg drivers will not work with KMS disabled. See the wiki page on your specific driver for details.